Methods of designing reverse geometry lenses for myopia control

ABSTRACT

Generating an aspheric contact lens design for facilitating myopia control of a cornea of a patient includes operations of: obtain measurement for degree refractive error of the eye in diopters; obtain measurement of one or more biomechanical properties of the cornea; define a diameter of a central zone of the contact lens based on pupil size; select a base curve profile and width for the central zone based on the refractive error and the one or more biomechanical properties; define a width of a reverse zone adjacent to and encircling the central zone, the width being greater than 0.5 mm; select a reverse curve profile for the reverse zone compatible with the base curve profile; modify the base curve profile adjacent to the reverse zone by applying a selected base eccentricity curve profile for enhancing the tension force strength of the reverse zone; define a width of a relief zone of the contact lens adjacent to and encircling the reverse zone; select a relief curve profile for the relief zone; define a width of an alignment zone of the contact lens adjacent to and encircling the relief zone; select an alignment curve profile for the alignment zone; and define a width of a peripheral zone of the contact lens adjacent to and encircling the alignment zone; select a peripheral curve profile for the peripheral zone; wherein the compression force strength and the tension force strength of the contact lens cooperate to reshape corneal curvature in a mid-peripheral region to address the myopia control when the contact lens is applied to the eye.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 15/988,079, filed on May 24, 2018, which is acontinuation application of U.S. patent application Ser. No. 15/441,763,filed on Feb. 24, 2017; the entire contents of which are herebyincorporated by reference herein.

FIELD

The present invention is related to contact lens design.

BACKGROUND

Near-sightedness, also known as short-sightedness or myopia, is acondition of the eye where light undesirably focuses in front of,instead of on, the retina. The improper positioning of the light focushas undesirable vision consequences, as distant objects appear blurrywhile close objects appear more normal. Experiencing blurry images canmanifest as headaches and eye strain. It is known for severenear-sightedness, increase in risk of retinal detachment, cataracts, andglaucoma can be experienced by the person. The underlying mechanism ofmyopia involves the length of the eyeball being too long or lesscommonly the lens being too strong, and as such can be characterized asa type of refractive error.

Myopia can be corrected with eyeglasses, contact lenses, or surgery,however such correction is short-lived as the degree of myopia for aperson's eyeball can increase over time, thus requiring changes to theirprescription eyeglasses and contact lenses. As surgery does not preventthe progression of myopia, additional surgeries may be required ifmyopia continues to develop. As such, eyeglasses are the easiest andsafest method of correction, eyeglasses are only a temporary correctivemeasure and therefore do not provide for myopia control, i.e. inhibitingthe progression of myopia (e.g. continual lengthening of the person'seyeball over time). Contact lenses can provide for myopia control (tosome degrees depending on the design of the lens) as well for myopiacorrection. The chance of myopia control may be limited with variousdegree of success depending on the formats used. However, all kinds ofcontact lenses may associate with a risk of infection due to closecontact with the corneal surface during application, which causesabrasion and scratching of the cornea eyeball. A properly designed lensmay reduce these risks. Refractive surgery can permanently change theshape of the cornea; however this type of correction suffers the samedisadvantages as eyeglasses when it comes to the lack of effectivemyopia control. Orthokeratology or overnight corneal reshaping uses theforces created under specially designed reverse geometry GP (gaspermeable) lenses, or molds, to temporarily change corneal shape formyopia reduction (correction). Normal vision can be achieved during theentire day with long term myopia controlling effect.

In terms of contact lenses for myopia control, a treatment zone (of thecontact lens) applies suction to the eyeball in order to reform theeyeball shape and thus decrease the length of the eyeball. However, thetreatment zone needs to have an increased strength for higher levels ofmyopia, however this also causes a disadvantage of the suction forcebeing too great and thus causes the contact lens to contact the surfaceof the eyeball and become stuck or otherwise attached thereon. Inextreme examples, it has been observed that a high myopia lens createsan audible popping sound when removed from the eyeball, clear evidenceof lens adhesion to the eyeball surface. Contact with the eyeball needsto be avoided, as this contact contributes to abrasion of the eyeballsurface tissues as the lens moves about the eyeball during eye movement(e.g. during REM—rapid eye movement), as well as when the lens isapplied or removed with respect to the eyeball. Known examples of lenstypes applied to myopia for orthokeratology are spherical and toric,however both of these lens types suffer from the disadvantage statedabove for higher levels of myopia, i.e. increased risk and occurrence oflens adhesion to the eyeball surface. Current state for the art formyopia lenses dictates that increasing suction levels are accomplishedvia decreasing the width of the fitting zone, however decreased widthscannot accommodate for manufacturing tolerances/errors of the lensmaterial as well as ability for the eyeball tissue to react (i.e.deform) properly to the applied suction forces. On the contrary,increased widths of the fitting zone can provide room for the eyeballtissue to react properly to the applied suction forces, as well as toinhibit manufacturing tolerances/errors of the lens material. Howeverincreasing the fitting zone width has the undesirable consequence ofreducing the strength of the suction force and thus making the lensineffective for treating myopia for higher diopter values.

SUMMARY

An object of the present invention is to provide a lens design methodand system to obviate or mitigate at least one of the above-presenteddisadvantages.

A first aspect provided is a method for generating an aspheric contactlens design for facilitating myopia control of a cornea of a patient,the method stored as a set of instructions in memory for execution by acomputer processor to: obtain measurement for degree refractive error ofthe eye in diopters; obtain measurement of one or more biomechanicalproperties of the cornea; define a diameter of a central zone of thecontact lens based on pupil size, the diameter being equal to or lessthan a selected dimension; select a base curve profile and width for thecentral zone based on the refractive error and the one or morebiomechanical properties, the base curve profile defining a compressionforce strength on the cornea when the contact lens is positioned on theeye, the base curve profile including a central zone tear layerthickness and a central zone radius of curvature; define a width of areverse zone adjacent to and encircling the central zone, the widthbeing greater than 0.5 mm; select a reverse curve profile for thereverse zone compatible with the base curve profile, the reverse curveprofile defining a tension force strength on the cornea when the contactlens is positioned on the eye, the reverse curve profile including areverse zone tear layer thickness and a reverse zone radius ofcurvature; modify the base curve profile adjacent to the reverse zone byapplying a selected base eccentricity curve profile for enhancing thetension force strength of the reverse zone, said applying contributingto the aspheric nature of the contact lens, the base eccentricity curveprofile including an aspheric zone tear layer thickness and an asphericzone base eccentricity; define a width of a relief zone of the contactlens adjacent to and encircling the reverse zone; select a relief curveprofile for the relief zone, the relief curve profile moderating thetension force strength adjacent to the relief zone, the relief curveprofile including a relief zone tear layer thickness and a relief zoneradius of curvature; define a width of an alignment zone of the contactlens adjacent to and encircling the relief zone; select an alignmentcurve profile for the alignment zone, the alignment curve profileincluding an alignment zone tear layer thickness and an alignment zoneradius of curvature; and define a width of a peripheral zone of thecontact lens adjacent to and encircling the alignment zone; select aperipheral curve profile for the peripheral zone, the peripheral curveprofile including a peripheral zone tear layer thickness and aperipheral zone radius of curvature; wherein the compression forcestrength and the tension force strength of the contact lens cooperate toreshape corneal curvature in a mid-peripheral region to address themyopia control when the contact lens is applied to the eye.

A second aspect provided is a lens design machine for generating anaspheric contact lens design for facilitating myopia control of a corneaof a patient, the machine including: a measurement device for obtainingmeasurement for degree refractive error of the eye in diopters and forobtaining measurement of one or more biomechanical properties of thecornea; a computer processor and memory having a stored as a set ofinstructions for execution by a computer processor to: obtainmeasurement for degree refractive error of the eye in diopters; obtainmeasurement of one or more biomechanical properties of the cornea;define a diameter of a central zone of the contact lens based on pupilsize, the diameter being equal to or less than a selected dimension;select a base curve profile and width for the central zone based on therefractive error and the one or more biomechanical properties, the basecurve profile defining a compression force strength on the cornea whenthe contact lens is positioned on the eye, the base curve profileincluding a central zone tear layer thickness and a central zone radiusof curvature; define a width of a reverse zone adjacent to andencircling the central zone, the width being greater than 0.5 mm; selecta reverse curve profile for the reverse zone compatible with the basecurve profile, the reverse curve profile defining a tension forcestrength on the cornea when the contact lens is positioned on the eye,the reverse curve profile including a reverse zone tear layer thicknessand a reverse zone radius of curvature; modify the base curve profileadjacent to the reverse zone by applying a selected base eccentricitycurve profile for enhancing the tension force strength of the reversezone, said applying contributing to the aspheric nature of the contactlens, the base eccentricity curve profile including an aspheric zonetear layer thickness and an aspheric zone base eccentricity; define awidth of a relief zone of the contact lens adjacent to and encirclingthe reverse zone; select a relief curve profile for the relief zone, therelief curve profile moderating the tension force strength adjacent tothe relief zone, the relief curve profile including a relief zone tearlayer thickness and a relief zone radius of curvature; define a width ofan alignment zone of the contact lens adjacent to and encircling therelief zone; select an alignment curve profile for the alignment zone,the alignment curve profile including an alignment zone tear layerthickness and an alignment zone radius of curvature; and define a widthof a peripheral zone of the contact lens adjacent to and encircling thealignment zone; select a peripheral curve profile for the peripheralzone, the peripheral curve profile including a peripheral zone tearlayer thickness and a peripheral zone radius of curvature; wherein thecompression force strength and the tension force strength of the contactlens cooperate to reshape corneal curvature in a mid-peripheral regionto address the myopia control when the contact lens is applied to theeye.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects will be more readily appreciated havingreference to the drawings, by way of example only, wherein:

FIG. 1 is a view of a lens design system for designing a gas permeablecontact lens for myopia control;

FIG. 2 is an illustrative force diagram of the lens of the system ofFIG. 1;

FIG. 3 shows example zones of the lens of the system of FIG. 1;

FIG. 4 shows an example configuration of the lens of the system of FIG.1;

FIG. 5 is shows a further example configuration of the lens of thesystem of FIG. 1;

FIG. 6 shows an example positioning of the designed lens on a cornea ofthe system of FIG. 1; and

FIG. 7 shows an example operation of the lens design of FIG. 1;

FIG. 8 shows example parameters of the tool of FIG. 1; and

FIG. 9 shows further example parameters of the tool of FIG. 1.

DETAILED DESCRIPTION

Referring to FIG. 6, corneal changes created by wearing orthokeratology(ortho-k) lenses 32 are not mechanical; rather, they are created viafluid forces exerted under the various curves of the posterior lenssurface with respect to the surface 34 of the eyeball 30. It is not astructural “bending” of the cornea surface 34, but rather aredistribution and relative thinning/thickening of the cornealepithelial cell layer due to forces exerted on the surface 34 as aresult of wearing of the lens 32 over a period of time. The effects(i.e. redistribution of epithelial tissue) of ortho-k can be temporary,but can provide excellent visual acuity for 12 to 48 hours followinglens 32 removal from the eye 30. The manipulation of the various curvesof the posterior surface provides for a controlled and predictablechange in the corneal topography that can result in improved unaidedvisual acuity (Controlled Clearance Philosophy). In addition, studieshave shown that the effects of ortho-k can be completely reversible.Upon discontinuing ortho-k treatment, for effective myopia control, therefraction (Rx of the eyes) and topography could return to the baseline.After a desirable number of ongoing treatment periods, it is therefractive change of the corneal tissue, post application of the lens 32(i.e. contributing to remolding of the corneal tissue as furtherexplained below), that provides for myopia control.

Referring to FIG. 1, shown is an illustrative lens design environment 10having a computer device 100 for implementing a lens design tool 102programmed via a set of lens design executable instructions stored instorage 114 of device infrastructure 116. The executable instructions ofthe design tool 102 are executed by a computer processor 108 of thedevice infrastructure 116. A user interface 112 of the computer device100 is used to receive design parameters 104 provided by a user (e.g.optometrist) of the system 10. The design parameters 104 are chosen bythe user based on patient eyeball 30 specifics (e.g. degree of myopia,corneal surface map, etc.). It is recognised that certain designparameters 104 can be measured and recorded by a corneal topographer110, for example. An output of the design tool 102 is a lens designspecification 120, specifying zone 50 (see FIG. 3) curve shape profilesand widths w, as well as tear film layer 36 thicknesses TLTi (see FIG.4). From the lens design specification 120, a reverse geometry contactlens 32 can be manufactured for subsequent application to the patient'seye 30, in order to effect myopia control as further discussed below.

As further discussed below, the design parameters 104 used by the lensdesign tool 102 can include measurements of eye surface geometry (i.e.surface shape of the eyeball), as well as biomechanical properties ofthe eye such as viscosity and rigidity. An example machine 110 formeasuring the eye surface geometry as well as the biomechanicalproperties could be an autorefractor or automated refractor as acomputer-controlled machine used during an eye examination to provide anobjective measurement of the eye for a person's refractive error andprescription for glasses or contact lenses. This can be achieved bymeasuring how light is changed as it enters a person's eye 30, repeatedin at least three meridians of the eye 30 and the autorefractorcalculates the refraction of the eye 30, sphere, cylinder and axis.Also, clinical devices 110, such as the Ocular Response Analyzer (ORA)or the Corneal Visualization Scheimpflug Technology (CorVis ST) can beused for measuring the corneal biomechanical properties of the eye 30,including corneal biomechanical parameters, axial length, and meankeratometry (i.e. K factor). Referring to FIG. 8, measured parameters104 for each eye 30 (i.e. Right and Left) can be such as but not limitedto: Horizontal and Vertical K readings related to Sphere diopter values(e.g. −4.00); Vertical K axis; eccentricity (recognising that aspherical eye curvature would have an eccentricity of 0); HorizontalVisible Iris Distance (HVID); and corneal diameter (which dictates theoverall Diameter dimension of the lens 32). The machine 110 can includemeasurement devices 111 such as but not limited to Topographic basedimaging measurement devices, air pressure generation devices, surfaceshape scanning devices, etc. It is recognized that the methodology ofdesigning the lens 32 as described herein via tool 102 could beprogrammed and implemented in the machine 110, as desired.

As further described below, the steps associated with FIGS. 7, 8, 9provide a particular solution to a problem or a particular way toachieve a desired outcome defined by the claimed invention, as opposedto merely claiming the idea of a solution or outcome. For example, thedescribed steps define a specific way, namely use of particular rules asimplemented via the executable instructions of the device(s) 100, 110 toobtain parameters 104 (measured or otherwise) to define overalldimensions and prescribed correction through defined zone widths andcurve profiles (e.g. curve radii) along with tear layer thickness TLT tosolve the problem of producing an appropriate lens design of desiredcorrective strength by forcing the width of the reverse zone to begreater than 0.5 mm while at the same time adjusting for decreases incorrective strength introduced by the reverse zone width being greaterthan 0.5 mm. It is recognised that conventional process is to increasethe corrective strength of the lens by selecting narrower and narrowerreverse zone widths, such that increasing of corrective strength isdirectly related to a decreasing of reverse zone width (i.e. less than0.6 mm). Contrary to state of the art thinking, the presently describedlens design via the tool 102 uses the defined rules to generateincreased corrective strength of the lens via selecting reverse zonewidths greater than 0.5 mm (e.g. 0.6 mm or greater due to 0.1 mmmanufacturing increment limits) while at the same time selecting higherlevels of base curve eccentric in the central zone (a or A and B) andrelief zone F, as further described below.

It is recognised that lower viscosity and higher rigidity corneal tissueof certain patients (with respect to a population norm) provides for areduced or delayed response to corneal tissue remolding facilitated bywearing of the designed lens 32. A further design parameter 104 suppliedto the design tool 102 is the myopia degree for the measured eye 30. Itis recognised that myopia, like all refractive errors, is measured indiopters (D), which are the same units used to measure the optical powerof eyeglasses and contact lenses. Lens powers that correct myopia arepreceded by a minus sign (−), and are usually measured in 0.25 Dincrements. The severity of nearsightedness is often categorized likethis: Mild myopia: −0.25 to −3.00 D; Moderate myopia: −3.25 to −6.00 D;High myopia: greater than −6.00 D. Further design parameters 14 caninclude prescription Rx, preoperative keratology K value readings,central corneal thickness (CCT), edge thickness (ET) & pupil size, whichcan affect the overall diameter of the lens 32 as well as selected curveprofile shapes of the zones 50 (see FIG. 3) and their correspondingwidths w. It is recognised that the diameter of the base opticaltreatment zone (zones A+B) can be 6.0 mm or smaller and can be as smallas 5.0 mm depending on the pupil size & the amount of targeting.Preferably the base optical treatment zone is 5.4 mm.

Referring to FIGS. 2, 3 and 4, contact lens 32 size is dictated by thesize (i.e. diameter) of the person's eyeball 30, thereby for myopiacontrol the available area for treatment, i.e. location of suctionforces, is dictated by the overall size of the treatment zone (zones Aand B and C and F) which leaves available space for the rest of thezones (e.g. alignment zone D, peripheral zone E, etc.). It is alsorecognised that the strength (i.e. steepness) of a reverse curve in thereverse zone C provides for the suction or tension force applied to theeye surface 34 of the person, for a given base curve of the central zoneA (providing the compression force) and a given alignment curve of thealignment zone D (providing for maintaining positioning or alignment ofthe lens on the eyeball). As such, the width of the reverse zone Ctypically dictates the strength of the tension force permissible, suchthat narrower widths (e.g. less than 0.6 mm such as 0.5 mm) result inthe creation of higher respective tension forces for a given reversecurve shape. As provided below, an alternative to using narrow widthfitting zones (i.e. less than 0.6 mm) to generate increased tensionforces, the present invention uses wider reverse zones C (e.g. 0.6 mm orgreater tending to decrease/lower the tension force in the reverse zoneC) which is then compensated for by 1) the application of a baseeccentricity curve shape to the base curve shape in the central asphericzone B adjacent to the reverse zone C and 2) the addition of a reliefzone F with relief curve shape situated between the reverse zone C andthe alignment zone D. The contribution of the application of the baseeccentricity curve shape is to increase the tension force generated bythe reverse curve via the introduction of the aspheric nature to thebase curve shape (which is spherical in nature). At the same time, theaddition of the relief zone F with associated relief curve shapeprovides for a reduction in the tension force experienced by the eye 30in the reverse zone C adjacent to the relief zone F.

Further to the above, based on manufacturing tolerances such that thezone width increments are provided in 0.1 mm increments, the reversezone C width We should be greater than 0.5 mm, e.g. 0.6 mm if only 0.1increments are provided for during lens manufacturing. In this case, asprovided below, an alternative to using narrow width fitting zones (i.e.less than or equal to 0.5 mm) to generate increased tension forces, thepresent invention uses wider reverse zones C (e.g. greater than 0.5 mmtending to decrease/lower the tension force) which is then compensatedfor by 1) the application of a base eccentricity curve shape to the basecurve shape in the central aspheric zone B adjacent to the reverse zoneC and 2) the addition of a relief zone F with relief curve shapesituated between the reverse zone C and the alignment zone D. Thecontribution of the application of the base eccentricity curve shape isto increase the tension force generated by the reverse curve via theintroduction of the aspheric nature to the base curve shape (which isspherical in nature). At the same time, the addition of the relief zoneF with associated relief curve shape provides for a reduction in thetension force experienced by the eye 30 in the reverse zone C adjacentto the relief zone F.

Referring again to FIG. 2, shown is a schematic representative view ofthe patient's eyeball 30 with positioned contact lens 32 adjacent to asurface 34 of the eyeball 30. Positioned between the lens 32 and thesurface 34 is a tear film layer 36 representing a layer of tear fluid(e.g. comprising lipid, aqueous, and mucin). It is recognised thatpresence of the tear film layer 36 inhibits adherence of the contactlens 32 to the surface 34, such that adherence is undesirable as it cancause inflammation and scratching of the eyeball due to motion of thecontact lens 32 about the surface 34 as the eyeball is moved relative tothe eyelid (not shown). As further discussed below, the shape profile(comprised of a number of curve regions 50—see FIGS. 4 and 5—withexample widths) of the contact lens 32 provides for areas of positive 37and negative 38 forces to promote movement 40 of the epithelium tissueof the eyeball 30 to facilitate control of myopia. The positive (push)forces 37 on the epithelium tissue work in conjunction with the negative(pull) forces 38 on the epithelium tissue to promote the movement 40. Itis recognised that pressure is defined as the force appliedperpendicularly to a surface 34 of the eyeball 30 per unit area of theeyeball 30 (which is therefore proportional to the width w of therespective zone 50, as further provided below). It is through theapplication of pressure to the eyeball 30 by the lens 32 that myopia iscontrolled, via the promotion of epithelium tissue movement 40 (e.g.molding of the epithelium tissue to conform towards the shape profile ofthe lens 32).

Referring to FIGS. 2 and 3 and 4, as such, the lens 32 is designedherein as a reverse geometry lens 32 (RGL) that reforms or moldsepithelium tissue through applying both compression and tension forcesat different sites across the corneal surface 34 through appropriatedesign of the width w and curve shape profile of different zones 50 (seeFIG. 3). The push-pull balance of the different zones 50 provides for apull-on of the tissues in the alignment zone D towards the reverse zoneC as directed via the relief zone F, as well as push-off of the tissuesin the treatment zone (zones A and B), while recognizing that theopposing forces 37,38 generated by the different zones 50 on the cornealtissue are coordinated into proper equilibrium through appropriateselection of design parameters 104 by a user of the lens design tool102. It is recognised that other forces at work on the corneal tissueinclude tear film layer 36 fluid forces as well as surface tensionforces (e.g. capillary forces) generated by the configuration of therelief curve in the relief zone F. As such, via equilibrium of theforces, the corneal tissue is remolded via the processes of squeeze filmforces (referred to as fluid jacket molding) provided by the tensionforces 37 as well as through hydrostatic pressure (referred to as vacuummolding), which are exerted via the tear film layer 36 positionedbetween the lens 32 and the eye surface 34. In general, the curve shapeprofiles of the different zones 50 act to provide for tension 37 (a pullforce on the corneal tissue) and compression 38 (a push force on thecorneal tissue) forces of various magnitudes, which are representativeand proportional to the thickness of the tear film layer 36. Forexample, a “steeper” curve profile (for example as provided in thereverse zone C) of the lens 32 generates a tension force 37 transmittedvia the tear film layer 36 on the surface 34 of the corneal tissue,recognizing that the steeper the curve (i.e. thicker the tear film layer36) the greater the tension force 37 generated. On the contrary, a“flatter” curve profile (for example in the middle of zone A near thecenter of the lens 32 or in the alignment zone D) of the lens 32generates a compression force 38 transmitted via the tear film layer 36on the surface 34 of the corneal tissue, recognising that the flatterthe curve (i.e. thinner the tear film layer 36) the greater thecompression force 38 generated. In general, the sum total magnitude ofthe compression forces 37 equal the sum total magnitude of thecompression forces 38 in order to provide for an equilibrium force lens32 design.

It is recognised that when the tear film layer 36 in the reverse zone Creaches approximately 60 microns, tiny bubbles or frothing can begin toform in the epithelial tissue, which promotes redistribution of theepithelial tissue. It is has been observed that if the tear film layer36 exceeds approximately 60 microns, larger bubbles can begin to form,which can create air space that can reduce the hydro-static pressure.Further, once pressure from central zones A+B begins to push tissue intothe reverse zone C, the air space decreases thus restoring the pressure.It is recognised that the zones A and B can be considered one zone withone applied curve extending from either side of the apex (point 0,0 inFIG. 4), rather than the two zones A and B having different respectivecurves, as further discussed below.

In implementation of the herein described lens 32 design, it isdesirable to select higher diopter values (e.g. −5 and higher) for evenlower levels of diagnosed myopia (e.g. −1 to −3), as typically the lowerlevels of myopia are associated with initial stages of the disease andthus are more easily controlled (i.e. myopia treatment at the earlystages is preferable to inhibit progression of myopia). As such, it isclear that increased tension forces 38 are desirable in the contact lens32 design, even for lower levels of myopia and therefore the asphericcontact lens 32 design (including a central zone A with applied baseeccentricity zone B, a fitting zone or reverse zone C, and a relief zoneF—see FIG. 3) is advantageous for all levels of myopia experienced by aperson. It is also recognized that proper selection of the width w ofthe reverse zone B is critical, as too small (i.e. less than 0.6 mm)increases the risk and occurrence of adhesion of the lens 32 to thesurface 34 for selected higher diopter values (e.g. −5 and higher).Therefore, the present lens 32 design takes advantage of wider reversezone C widths w (i.e. greater than 0.5 mm, e.g. 0.6 mm given 0.1 mmincrements due to manufacturing tolerances/techniques), while at thesame time compensating for inherent reductions in the tension force 38(as a consequence of the selected wider width w contributing to aproportionately greater unit surface area of tension force application)by application of a base eccentricity curve in the aspheric zone B (orin both Zones A and B) in combination with application of a relief curvein the relief zone F, as further described herein. Further, it isrecognised that since the overall dimension of the lens 32 is limited tothe size of the person's eyeball 30, selection of a diameter of thecentral optical zone A+B (e.g. 5.4 mm) should be done in order toprovide room for the wider reverse zone C (e.g. 0.6 mm or greater, orotherwise greater than 0.5 mm) along with the additional relief zone Fused to create a surface tension force 38 or capillary force in therelief zone F in order to suck/move 40 or otherwise direct the eyeball30 tissue from an alignment zone D and into/towards the reverse zone C.It is also recognised that using a larger central optical zone A+B (e.g.greater than 5.4 mm) without the application of the base eccentricitycurve in the aspheric zone B (or in both Zones A and B) could also causeimproper application of the tension force 38 in the vicinity of the edgeof the central optical zone A+B (i.e. adjacent to the reverse zone C)and therefore could also contribute to the risk/occurrence of lensadhesion. As such, it is recognized that utilization of a relief zone Fand an aspheric zone B (or in both Zones A and B) in the lens 32 designfacilitates the proper application of appropriate suction pressure inthe reverse zone C (to accommodate the desired maximum correctionsetting) while at the same time inhibiting adhesion of the lens 32 tothe surface 34.

Referring to FIGS. 3 and 5, shown is an example contact lens 32 having aplurality of zones 50 of defined width w; namely a back optical zone A,an aspheric zone B, a reverse zone C, a relief zone F, an alignment zoneD and a peripheral zone E. It is recognised that zones A and B can betreated as one aspheric zone and thus have only aspheric curve(s)applied to both zones A and B as desired. Each shape profile (i.e.curve) for each of the zones 50 is generated using respective curveprofile equations, given by example below. It is recognised that thereare shortfalls to achieve a desired result of myopia control. The mainreason being many unknowns are involved with curve parameters and theiradjustment needed for effective results in control. In order tofacilitate myopia control, each individual curve (for each of the zones50) serves different functions and they are all linked together as awhole entity to provide the desired outcome of myopia control. Thefollowing provides a summary of each of the zones 50 and an examplerespective curve profile equation, such that all zones 50 are listedwith their individual function and how they cooperate upon each other toenhance the result (i.e. promote appropriate movement 40 (see FIG. 2) ofthe epithelium tissue of the eyeball 30 when the contact lens 30 isapplied to the surface 34 of the eyeball 32.

Referring to FIG. 4, for example, each of the curve parameters for eachof the zones 50 could include 1) a selected curve radius Ri (e.g. theradius of a sphere to one side of the lens 32 such that higher the Rithe flatter the curvature of the lens in the respective zone 50 regionand/or the higher the R the steeper the curvature of the lens in therespective zone 50 region), 2) a selected tear film layer thickness 36(TLTi being the desired distance of the lens 32 material of the zone 50from the surface 34 of the eye 30 and 3) a selected zone width Wirepresenting the width of the respective zone 50 as a portion of thetotal lens width Wt (see FIG. 3). In geometry, the center of curvatureof a curve is found at a point that is at a distance from the curveequal to the radius of curvature lying on the normal vector, such thatit is the point at infinity if the curvature is zero. A zone 50 of thelens 32 has a center of curvature Ri located in (x, y, z) either alongor decentered from a system local optical axis X. The vertex V of thelens surface is located on the local optical axis X. The distance fromthe vertex V to the center of curvature is the radius of curvature Ri ofthe lens 32 surface. The sign convention for the optical radius ofcurvature is as follows: if the vertex V lies to the left of the centerof curvature, the radius of curvature Ri is positive. If the vertex Vlies to the right of the center of curvature, the radius of curvature Riis negative. In the case of the RGL lens 32, the radii of curvature Riare positive.

Zone A

The Back optical zone A containing a base curve is defined as a firstportion of the treatment zone related to the pupil size of the eyeball30. This zone A of the contact lens 32 generates a compression force 37for flattening of the central cornea of the eyeball 32 and creates asteepening effect of the mid peripheral cornea. An example curve profilefor the zone A of a spherical shape is:

1) zone A radius of curvature Ra, 2) zone A width Wa, and zone A tearlayer TLTa.

It is recognised that increasing the steepness at the mid peripheralcornea of the eyeball 30 can provide more plus power to facilitate aperipheral myopia defocus result. The steepness can be about 1 to 1.5times the amount of central flattening. For example, at least 2-3 timessteeper than that of central flattening (e.g. with central correction of4.0 D, at 3 mm treatment zone, the plus power generated is about 2.0diopters D, whilst for 5-6 mm zone, the add can go up to 8-12 dioptersD). Hence the amount of mid periphery plus power increases with pupilsize (for the treatment zone), however it is recognised that too large atreatment zone can have a diminishing effect of clear central vision. Itcan be difficult to increase the mid peripheral plus power whilemaintaining a small treatment zone if we are not targeting extra powerat the central zone A (targeting extra power can result inover-correction during the day). Any change in size of zone A can causea major re-calculation of all other lens 32 parameters. Optimal size hasto be used for effective myopia control result but could also considermaking room for the rest of the curves 50 (i.e. other than zone A). Asdiscussed above, calculation of the radius Ra can be done using theaspheric equation z(r) provided below, such that both the curves in zoneA and zone B are aspheric in nature.

Zone B

A second portion of the treatment zone is the aspheric zone B having aselected base eccentricity ranging from 0.5 to >1.6 (noting theeccentricity of a sphere is defined as zero). Fluid clearance (i.e. tearfill layer 36) in this zone B is important since a zero apical clearance(i.e. zero tear layer thickness) can cause lens 32 decentration whichcan create lens adhesion & corneal abrasion of the eye surface 34. Assuch, increasing levels of aspheric in the zone B provide for flattening(i.e. decreasing the radius) of the aspheric curve profile shape ascompared to the spherical curve profile shape of in the zone A (i.e.curve radius in zone A is greater than curve radius in zone B).

An example curve profile for the zone B of an aspherical shape is,referring to FIG. 4: 1)

${{z(r)} = {\frac{r^{2}}{R\left( {1 + \sqrt{1 - {\left( {1 + \kappa} \right)\frac{r^{2}}{R^{2}}}}} \right)} + {\alpha_{4}r^{4}} + {\alpha_{6}r^{6}} + \ldots}}\mspace{14mu},$

such that the optic axis in this case lies in the z direction and thez(r) is the sag—the z component of the displacement of the surface fromthe vertex, at a distance r from the axis. The coefficients describe thedeviation of the surface from an axially symmetric quadratic surfacespecified by R and k. The example curve profile for the zone B (or forzones A and B) would also include zone B width Wb, and zone B tear layerTLTb (or for zones A and B of both aspheric nature also including thezone A width Wa, and zone A tear layer TLTa).The optical nature of an aspheric lens is such that the aspheric zone B(or zones A and B) creates a small central aperture of distant viewing.The aspheric zone B size of about 1.5 to 3.0 mm diameter (or zones A andB of approximately 5.4 mm), for example. Different from a spherical zone(eccentricity of zero), an aspheric curve provided by the aspheric zoneB (or zones A and B) progressively flattens from the central zone A (orfrom the apex at 0,0) towards the edge of aspheric zone B connected to areverse zone C adjacent to the aspheric zone B. The effect ofpositioning the aspheric zone B between the central zone A (or zones Aand B) and the reverse zone C creates an effect of progressivelydiminishing minus power towards the periphery (hence increasing pluspower at the reverse zone C and creating a considered high order ofspherical aberration). However, one needs to be careful with theapplication of aspheric zone B (or zones A and B), as it is highlyrelated to the size of the back optical zone A (or zones A and B). For ahigher relative asphericity with larger back optic zone A (or zones Aand B), the forces generated can be too high/large to create undesiredresult such as lens 32 binding and adhesion to the surface 34 (see FIG.2). The contact lens design methodology (as implemented via the programinstructions—see FIG. 1) directs the user to the correct asphericity andzone B size based (or zones A and B) on selected parameters as furtherexplained below. Further, the aspheric zone B (or zones A and B) cancreate even and smooth central applanation (otherwise known asflattening of the convex surface 34) at the center to provide clearvision and inhibit any mixed astigmatism during treatment (i.e.application of the designed lens 32 to the eyeball 30). As such it isrecognised that the treatment zone of zones A and B can be provided asaspheric in shape in the lens 32).

Zone C

The reverse zone C is considered the most powerful zone in terms offorces 36,37 generation providing for a negative tear film 36 dynamic.The reverse zone C serves to pile up (i.e. movement 40—see FIG. 2) morecorneal tissues of the eyeball 30 from the treatment zone (zones A andB) towards the reverse zone C.

An example curve profile for the zone C shape is:

1) zone C radius of curvature Rc, 2) zone C width Wc, and zone C tearlayer TLTc.

The reverse zone C is related to and is responsible for lens 32steepness and flatness with the force 38 generated (tension and squeezefilm force) and is provided as a reciprocal of the curves for zones Aand B. In application of the designed lens 32 to the eyeball 30, whentension force (i.e. pressure) increases, the cornea 30 is molded to theback surface of lens 32. If the tear layer thickness (TLT) 36 in thereverse zone C and apical clearance (TLT of the zones A and B) areinaccurate, the cornea 30 tissues cannot accurately mold to the basezone A/B, thereby affecting refractive changes. The tension forces 38generated in this zone C are largely dependent on the width w (size) ofthe zone C (see FIG. 2). The narrower the zone C, the larger the force38 generated and vice versa. Generally speaking, this width w typicallydictates the strength of the total permissible forces 37,38 of the lens32 design.

Bearing the above in mind, the lens 32 design provided herein applies toa width w of the reverse zone C greater than 0.5 mm (e.g. 0.6 mm) as ageneral rule (the default value), recognizing that any width w less than0.6 mm (e.g. 0.5 mm or less for 0.1 mm increments) can createundesirable excessive forces 38 of the zone C that can promote adhesionof the lens 32 to the surface 34 (when including the compression force37 of the base optical zones A and the forces 37 generated in theaspheric zone B (or zones A and B). The value of the forces 37 isadjustable based on the calculation from the computer processor usingthe reverse zone C equation and other patient/lens parameters suppliedby a user of the lens design system 10. If an increased tension force 37is desired, the amount of base eccentricity of the aspheric zone B (orzones A and B) can be increased to reach the desired results or viceversa. This should satisfy the SAG philosophy. If this curve is tooflat, len's SAG is inadequate. If too steep, the len's SAG is too greatand the lens 32 could be pushed away from the corneal 30 apex, therebylessening the molding effect of the epithelium tissue movement 40 (e.g.molding of the epithelium tissue to conform towards the shape profile ofthe lens 32). Too wide of a zone C could diminish the desired moldingeffect. The size of the zone C is dependent on the amount of targetingof extra correction of myopia from the original value (i.e. a change indiopter value of the patient eyeball as obtained during myopiadiagnosis). Any changes in the curve of this zone C can also change thefitting characteristics of all zones peripheral to it (i.e. the reliefzone F and the aspheric zone B). The value of the tear volume in thiszone C to create any desired tension force 38 can also depend on the CH,CRF (what are these?) and corneal center thickness (CCC) of the cornea30. Computer processes will guide the fitter for the best requiredvalues. Most of the time, an increase to the force in this zone C isused in order to satisfy the peripheral defocus result desired formyopia control. When the force 37 reaches a level that may cause cornealproblems (adhesion & binding), it can then be relieved to some extent tosatisfy the tear film equilibrium and to avoid any health problem viaapplication of the relief zone F.

Zone F

The relief zone F can be considered as an enhancement curve. This reliefcurve is situated in between the reverse zone C and the alignment zoneD.

An example curve profile for the zone F shape is:

1) zone F radius of curvature Rf, 2) zone F width Wf, and zone F tearlayer TLTf.

Other than providing a reduction in tension forces 38 at the reversezone C (to relieve some excessive pressure in this zone C at the edgesof the zone C), the relief zone F also serves to generate extra forces(small capillary forces and surface tension forces) used to bridge thezones C and D to effectively gather and move 40 corneal tissues from thealignment zone D adjacent to the relief zone F and towards the peripheryof the reverse zone C. Finally, the relief zone F also serves to balancethe tear force equilibrium between the reverse curve of the reverse zoneC and alignment curve of the alignment zone D. The relief curve profileof the relief zone F is an important design consideration in view of theabove-discussed functions.

Zone D

The alignment zone D can be comprised of one or more individualalignment curves (e.g. 3), which provide for the overalltightness/looseness fitting of the designed lens 32 with respect to thesurface 34.

An example curve profile for the zone D shape is (recognising there canbe more than one alignment curve of differing profiles in the alignmentzone D):

1) zone D radius of curvature Rd, 2) zone D width Wd, and zone D tearlayer TLTd.

The alignment zone can contain the first curve(s) to be determined bythe design tool 102, when starting to construct the lens 32, in order toprovide for appropriate lens 32 movement and assist in centration duringlens 32 wear by the patient. The width(s) w of the alignment zone Dcurve(s) can be adjusted to optimize room for the other curves in theother zones 50. For example, design tool 102 can provide for theconstruction of a plurality (e.g. 3) of different the alignment zones Dwith various radii (i.e. curve profile) and tear film layers. The sizesof the zones D can be designed based on the corneal surface conditionssuch as the toricity, eccentricity, pressure created by lid tension andpositioning. The computer processor of the design tool 102 can help thetool user to determine the proper width w and TLT 36 under the zones Dfor forces 38 equalization. Compression forces 38 generated at thiszone(s) can be lower than those tension forces 37 of the reverse zone C.The computer processor can help to determine the surface tension andcapillary forces of this zone(s) D to build up tissues at via movement40 towards the reverse zone C while facilitating the maintaining ofappropriate positioning of the lens 32 while inhibiting adhesion of theunderside of the lens 32 to the surface 34 of the eyeball 30. It isrecognized that both the reverse and alignment curves satisfy sagittalequivalency in order for the lens 32 to provide for corneal moldingduring application of the lens 32. It is also recognised that the widthof zone D, i.e. Wd, can be used to make room for the desired forces andwidths of zones A, B,C, F providing for the majority of the treatment inthe treatment zone. In other words, once the curve radius Ri and widthparameters Wi have been selected for the zones A, B, C, F, the radius Rdand width Wd for the zone D can be selected in order to balance thedesired overall Diameter of the lens 32 (i.e. as dictated by the overallmeasured dimensions of the patient's eye 30).

Zone E

The peripheral zone E is located at the edge of the lens 32 and as suchis the furthest zone 50 from the central optical zone A.

An example curve profile for the zone E shape is:

1) zone E radius of curvature Re, 2) zone E width We, and zone E tearlayer TLTe.

The peripheral zone E facilitates lens 32 centration. Further, tearmeniscus at the edge of lens 32, when in contact with air, can produce anegative or tension force 38. Accordingly, the curve of the peripheralzone E serves to control excessive lens adherence to corneal surface forlens centration. Proper calculation (via the computer processor usingthe peripheral zone curve) determines the amount of tear reservoiravailable to move under the lens 32, and to facilitate tear continuityand flow under the lens 32 surface. As long as the TLT 36 under the lens32 inside the peripheral zone E is sufficient and balanced, a seal-offlens can enhance centration.

It is recognised in the above that a radius of curvature Ri is chosenfor each of the zones A,B,C,D,E,F however it is recognised that morecomplex curve shapes (e.g. having multiple or variations on a singleradius) can be substituted as desired.

In view of the above, all zones 50 have to work together in order tohave a construction of the lens 32 with balanced forces 37,38 foreffective result of the corneal molding. The computer processor canprovide for calculations for this purpose via usage of the appropriatecurve(s) profile shape assigned to each zone 50. As such, given theabove, it is recognised that contact lens 32 size is dictated by thesize of the person's eyeball 30, thereby for myopia control theavailable area for treatment, i.e. location of suction forces 38, isdictated by the overall size of the treatment zones A, B, C,F whichleaves available space for the rest of the required zones (e.g.alignment D, peripheral E). It is also recognised that the strength(i.e. steepness) of the reverse curve of the reverse zone C provides forthe suction or tension force 38 applied to the eyeball 32 of the personin the reverse zone C, for a given base curve of the central opticalzone A (providing the compression force 38) and a given alignment curveof the alignment zone D (providing for maintaining positioning oralignment of the lens 32 on the eyeball 30). As such, the width w of thereverse zone C typically dictates the strength of the tension force 37permissible, such that narrower widths w (e.g. less than 0.6 mm such as0.5 mm) result in the creation of increased tension forces 37 for agiven reverse curve shape. As provided below, an alternative to usingnarrow width reverse zones C (i.e. less than 0.6 mm) to generateincreased tension forces 37, the present design tool uses wider reversezones C (e.g. 0.6 mm or greater tending to decrease/lower the tensionforce 37) which is then compensated for by 1) the application of a baseeccentricity curve shape of the aspheric zone B to the base curve shapein the central zone A (or for both zones A and B) adjacent to thereverse zone C and 2) the addition of the relief zone F with reliefcurve shape situated between the reverse zone C and the alignment zoneD. The contribution of the application of the base eccentricity curveshape (e.g. of both zones A and B) is to increase the tension force 37generated by the reverse curve via the introduction of the asphericnature to the base curve shape (which can be spherical in nature). Atthe same time, the addition of the relief zone F with associated reliefcurve shape provides for a reduction in the tension force 37 experiencedby the eyeball 30 in the reverse zone D region adjacent to the reliefzone F, thereby assisting in the inhibition of adhesion of the lens 32to the surface 34.

Finally, this lens design tool 102 can also help to modify the fittingcondition to allow the lens 30 to sit properly on the eyeball surface34, and to reach equilibrium. You can evaluate a fitting correlationbetween the cornea 30 and the contact lens 32 by the sagittal depth(sag) correlation between the cornea 30 and the contact lens 32. In acontact lens 32, sag defined as a perpendicular line from the apex ofthe lens 32 to a line intersecting the diameter of the lens 32. The goalof custom lens 32 fitting is the proper alignment of the posterior lens32 surface to the surface 34 of the cornea 30. This is what normallycalled Lens SAG equilibrium and is important for lens 30 constructionbased on the design. For the custom designed lens 32 of FIG. 2, Lens sagcan be defined as the sagittal height of each of the individual zones 50of the lens 32 added together. The sag of the lens 32 is equal to thesag of the zones A+B radius/sag zones A+B diameter (R of A+B)/(D ofA+B), plus the sag of the reverse zone C over its width, and plus thesag of the alignment zone D. The sag of the lens 32 can be measured tothe diameter that represents the common chord of contact between thelens 32 and the corneal surface 34.

Referring to FIGS. 7, 8, 9 shown is an example operation of the system10 of FIG. 1. At step 150, the machine 110 takes measurements of the eye30 parameters 104 (e.g. obtain measurement of one or more biomechanicalproperties of the cornea). At step 152, the preference parameters 104can be input by the doctor based on patient data (e.g. measured eyediameter) such as desired lens diameter (related to corneal diametermeasurement), maximum corrective power (e.g. −6.5 for a measured −4Dioper reading of the patient eye(s) 30 as an obtained measurement fordegree refractive error of the eye 30 in diopters), base TLT for theapex in zone A (e.g. apical TLT) based on strength of the correction(e.g. higher corrections can dictate larger apical TLT), base curveeccentricity (as dictated by the measured Eccentricity in FIG. 8) suchthat an increase in base curve eccentricity results in an increase inaspheric shape of zone B (or zones A and B) and thus an increase inrespective forces 37,38 in the zones A and B (and C and F for balancingreverse and relief curves). As noted, a default value of Reverse CurveWidth of 0.6 (e.g. greater than 0.5 mm) can be maintained or changed asdesired.

At step 154, the software tool 102, via the computer processor 108 (seeFIG. 1) can calculate the radii of the various curves for the zonesA,B,C,D,E,F as noted above, based on the selected parameters 104 (e.g.base curve eccentricity, Optical Zone, Apical TLT, etc.). It isrecognised that for various widths Wi not actively selected by thephysician (e.g. user of the tool 102), the software tool 102 can providedefault values retrieved from memory 114). It is also recognised thatthe preference parameters 104 can be input before or after calculationof the widths Wi and curve radii Ri is performed, for example in aniterative fashion as the user fine tunes the lens 32 design using theprovided default values and adjustable values of the tool 102 in orderto design the lens 32 abiding by the overall lens diameter (dictated bythe actual eye size), the degree of correction required (dictated by themeasured patient prescription and K readings), as well as the measuredEccentricity of the eye, recognizing that each lens 32 for each eye 30of the patient can have different lens designs due to differingparameter 104 measurements. At this step the user can define/select adiameter of the central zone of the contact lens 32 based on pupil size,the diameter being equal to or less than 5.4 mm as part of the overalllens diameter Wt. At this step the user can define/select a diameter ofthe central zone of the contact lens 32 based on pupil size, thediameter being equal to or less than 5.5 mm as part of the overall lensdiameter Wt. At this step the user can define/select a diameter of thecentral zone of the contact lens 32 based on pupil size, the diameterbeing equal to or less than 5.6 mm as part of the overall lens diameterWt. At this step the user can define/select a diameter of the centralzone of the contact lens 32 based on pupil size, the diameter beingequal to or less than 5.7 mm as part of the overall lens diameter Wt.

Also shown in FIG. 9 is the Target Lens Power of 2.00 (by example, whichis referred to by a person skilled in the art as the Jesson factor.Referring to FIG. 8, the sphere measurement is the measure prescription(e.g. Rx), the Eccentricity (e.g. 0.25) is the actual measured asphericshape of the patient's eye 30 (recognizing an eccentricity of 0 woulddenote a spherical shape hence no aspheric nature), the Cylinderrepresents a measurement of astigmatism of the eye 30 and Axisrepresents the axis measurement of the astigmatism.

As part of step 154, the executable instructions can be used tofacilitate the method for generating the aspheric contact lens design120 for facilitating myopia control of the cornea of the patient byselecting a base curve profile and width for the central zone (e.g.zones A and B) based on the refractive error and the one or morebiomechanical properties, the base curve profile defining a compressionforce strength on the cornea when the contact lens is positioned on theeye, the base curve profile including a central zone tear layerthickness TLT and a central zone radius of curvature R; define a widthWr of a reverse zone C adjacent to and encircling the central zone A,B,the width being greater than 0.5 mm; select a reverse curve profile forthe reverse zone C compatible with the base curve profile, the reversecurve profile defining a tension force strength on the cornea when thecontact lens 32 is positioned on the eye 30, the reverse curve profileincluding a reverse zone tear layer thickness TLTr and a reverse zoneradius of curvature Rr; modify the base curve profile adjacent to thereverse zone C by applying a selected base eccentricity curve profilefor enhancing the tension force strength of the reverse zone C, saidapplying contributing to the aspheric nature of the contact lens 30, thebase eccentricity curve profile including an aspheric zone tear layerthickness TLT and an aspheric zone base eccentricity in the zone(s) A,B;define a width Wf of a relief zone F of the contact lens 32 adjacent toand encircling the reverse zone c; and select a relief curve profile forthe relief zone F, the relief curve profile moderating the tension forcestrength adjacent to the relief zone F, the relief curve profileincluding a relief zone tear layer thickness TLTf and a relief zoneradius of curvature Rf. It is recognised that the pressure exerted inthe corneal tissue in zone F is less than the pressure in zone C andgreater than the pressure in zone D.

It is recognised that the software tool 102 calculates the lens design(e.g. zone width Wi, TLTi, radii Ri) based on the base curveeccentricity (affecting zones A,B) and other parameters 104 (e.g.overall lens width Wt, maximum correction, etc), recognizing thatselecting an increase from the given/current/default value of the design(e.g. TLTi, radii Ri) typically results in an increase in the forcesgenerated for that respective zone 50. Conversely, an increase in thezone width Wi from the given/current/default value of the lens designwould result in a decrease in the forces generated for that respectivezone 50, which if not desired as such, would provide for a change asincrease in the TLTi and/or radius Ri of that zone to compensate (i.e.reraise the forces that were decreased via the increased change in widthWi of the zone 50).

It is recognised that the software tool 102 calculates the lens design(e.g. zone width Wi, TLTi, radii Ri) based on the base curveeccentricity (affecting zones A,B) and other parameters 104 (e.g.overall lens width Wt, maximum correction, etc), recognizing thatselecting an decrease from the given/current/default value of the design(e.g. TLTi, radii Ri) typically results in a decrease in the forcesgenerated for that respective zone 50. Conversely, a decrease in thezone width Wi from the given/current/default value of the lens designwould result in an increase in the forces generated for that respectivezone 50, which if not desired as such, would provide for a change as adecrease in the TLTi and/or radius Ri of that zone to compensate (i.e.lower the forces that were increased via the decreased change in widthWi of the zone 50).

In view the above, it is recognised that selection of any of theparameters 104 via the tool 102 that results in a desired increase inthe forces for a particular zone 50 would not have to be compensated forby selection of other parameters 104 in order to correspondingly lowerthe raised force(s). Further, in view the above, it is recognised thatselection of any of the parameters 104 via the tool 102 that results ina desired decrease in the forces for a particular zone 50 would not haveto be compensated for by selection of other parameters 104 in order tocorrespondingly increase the raised force(s). Accordingly, one shouldrecognize the interdependence of the parameters 104 and thus theirinfluence on the forces for a given zone 50 as well as their influenceon the forces design for adjacent zones 50 of the lens 32. For example,increases in the prescription Rx (e.g. raising the maximum correctionforce of the lens 32) typically results in a widening of the relief zonewidth Wf along with an increase in the TLTf of the zone F in order tofacilitate an increase in gathering of corneal tissue from the alignmentzone D while at the same time helping to inhibit adhesion of the lens 32to the surface 34 of the eye 30 due to forces 37,38 present in the zonesA,B,C reflecting the desired maximum correction power. It is alsorecognised that based on the pressure generated by the forces in thezone F, the magnitude of the pressure in the zone D (generated by theforce resulting from the selection of Rd, Wd, TLTd) could be adjustedsuch that the pressure in zone D is always less than the pressure inzone F. It is also recognised that the pressure generated in zone D canbe provided by section of the parameters Rd, Wd, TLTd such that suctionforces are present to promote gathering of the corneal tissue from thealignment zone D and towards the relief zone F while at the same timeinhibiting adhesion of the lens 32 in the vicinity of the zone D to theeye surface 34, recognizing if the suction forces in zone D are below aset D gathering threshold then the desired gathering of corneal tissuewould be negligible while if the suction forces in zone D are below aset D adhesion threshold then the lens is prone to adhesion during wear.

At step 156, the alignment zone D can be adjusted in order to accountfor the selected curve profiles of zones A, B, C, F, recognising thatzone D facilitates both alignment of the lens 32 on the eye 30 as wellas facilitating gathering of corneal tissue from the alignment zone Dtowards the reverse zone C (via the relief zone F) due to requisitesuction forces provided by the curve D profile. For example, define awidth of the alignment zone D of the contact lens 32 adjacent to andencircling the relief zone F in order to equate the Lens diameter Wtequal to the selected diameter (e.g. reducing the alignment zone widthWd in order to match the selected lens diameter or increasing thealignment zone width Wd in order to match the selected lens diameter);and select the alignment curve profile for the alignment zone D, thealignment curve profile including an alignment zone tear layer thicknessTLTd and an alignment zone radius of curvature Rd. It is recognised thatthat the TLTd as well as the radius Rd can be adjusted in order toprovide for an appropriate level of suction forces 37—see FIG. 2—in thiszone D, recognising that too great a suction force can result inadhesion of the lens 32 to the eye surface 34 while too low a suctionforce (below a set D gathering threshold) can result in an undesirablemagnitude of movement of the lens 32 when applied to the eye 30 and/or aloss in ability to gather corneal tissue towards the relief zone F. Itis recognised that as well, the TLTi of the various zones can beadjusted, such that a greater TLTi than the current setting results in alarger separation distance of the lens 32 from the corneal surface 34and/or a greater force provided for in the respective zone 50 than thecurrent setting. In general it is recognized that as the magnitude ofthe width We of the reverse zone C is raised above 0.5 mm, the greaterthe base curve eccentricity that must be applied to the curve profile(e.g. radius) in zones B or A and B, in order to provide for the maximumcorrection as specified in the parameters 104.

At step 158, the user can define or otherwise confirm the width We ofthe peripheral zone E of the contact lens 32 adjacent to and encirclingthe alignment zone D and select a peripheral curve profile for theperipheral zone E such that the peripheral curve profile includes aperipheral zone tear layer thickness TLTe and a peripheral zone radiusof curvature Re.

At step 160, the parameters 104 can be adjusted in order to recalculatethe curve profiles including the radii Ri, the widths Wi and the TLTi ofthe zones A,B,C,D,E,F in order to balance the forces 37,38 to providefor the desired maximum corrective power (via forces generated by thezones A,B,C,F) as well as providing for appropriate positioning andalignment of the lens 32 (via forces generated in zone D) as well asproviding for appropriate peripheral forces in zone E. Once one or moreof the parameters 104 are readjusted, any or all of steps 152 5 158 canbe repeated buy the software tool 102. For example, one of the adjustedparameters could be the reverse zone width Wr, thus resulting in alowering of the forces in the reverse zone C for the given TLT r andradius Rr and thus require an adjustment in zones A and/or B (e.g.increase in the base curve eccentricity in zones A and/or B, an increasein the TLTa and/or TLTb) and/or an adjustment in the reverse zone C(e.g. increase in the TLTr and/or steeper radius Rr), in order toprovide for the desired maximum correction power as specified in theparameters 104 (see FIG. 9—e.g. −6.5). It is also recognised that as aconsequence of adjustment, the width Wf of the relief zone F could beadjusted (e.g. made wider than the current setting, made narrower thanthe current setting) as well as the width Wd of the alignment zone couldbe adjusted (e.g. made wider than the current setting, made narrowerthan the current setting). It is also recognised that as a consequenceof adjustment, the width TLTf of the relief zone F could be adjusted(e.g. made taller than the current setting, made shorter than thecurrent setting) as well as the TLTd of the alignment zone Wd could beadjusted (e.g. made taller than the current setting, made shorter thanthe current setting). Once completed, i.e. the parameters 104 arefinalized, the lens design is output at step 162 for use in manufactureof the physical lens by a lens making machine according to thecalculated cure profiles as noted above.

Referring to FIG. 8, the software tool 102 can provide via the userinterface 112 (see FIG. 1) various controls 105 for adjusting theparameters 104, e.g. making the radii of selected zones 50 (see FIG. 3)either progressively steeper or flatter, recognising that steeperresults in an increase in the respective zone 50 force 37,38 whileflatter results in a decrease in the respective zone 50 force 37,38. Itis recognised that the adjustments can be made separately for the Rightand Left eye lenses 32.

Further, the above steps can include the at least one biomechanicalproperty 104 is selected from the group consisting of central thickness,hysteresis and rigidity of the cornea. Further, the above steps caninclude adjusting the reverse curve profile to account for the at leastone biomechanical property. Further, the above steps can include thealignment curve profile is selected before the reverse curve profile.Further, the above steps can include the alignment curve profile isselected after the reverse curve profile. Further, the above steps caninclude adjusting at least one of the reverse curve profile, the reliefcurve profile or the alignment curve profile such that the pressureexerted in the reverse zone is greater than the pressure exerted in therelief zone which is greater than the pressure exerted in the alignmentzone to facilitate gathering of corneal tissue from the alignment andrelief zones towards the reverse zone.

It is recognized that the steps provided above with regard to FIGS. 7,8, 9 can be programmed into the machine 110 having measurement devices111 for measuring the eye surface geometry as well as the biomechanicalproperties 104, in order to provide for an integrated machine of eyemeasurement and lens design. As such, the computing device 101 of FIG. 1can include the machine 110, as an integrated device and/or as separatedevices coupled together to provide for an end to end solution of eyemeasurement and resulting lens 32 design 120 based on the measuredparameters 104. As such, the machine 110 would be coupled to orotherwise have respective processor(s) 108, user interface 112, deviceinfrastructure 116 executable instructions (e.g. for implementing themethod described herein of lens 32 design as well as for performingmeasurement and recording via storage 114 of the eye parameters 104) aswell as memory 114. It is recognized that user of the device 100,110would be facilitated via the measurements 104 and the design parameters104 of the software tool 102 to take measurements of a patient's eyes 30and then design appropriate lens 32 to provide during wearing of thelenses 32 the compression force strength and the tension force strengthof the contact lenses to reshape corneal curvature in a mid-peripheralregion of the patient's eyes 30 to address the myopia control.

Referring again to FIG. 1, the computer device 100 can comprises aland-based network-enabled personal computer. However, the invention isnot limited for use with personal computers. For instance, one or moreof the network devices 100 can comprise a wireless communicationsdevice, such as a wireless-enabled personal data assistant, a tablet, ore-mail-enabled mobile telephone if a network is configured to facilitatewireless data communication. The computer device 100 can include thenetwork connection interface 118, such as a network interface card or amodem, coupled to the device infrastructure 116. The connectioninterface 118 can be connectable during operation of the computer device100 to a network (e.g. an intranet and/or an extranet such as theInternet), which enables the devices to communicate with other computerdevices as appropriate. The computer device 100 can also have the userinterface 112, coupled to the device infrastructure 116, to interactwith a user (e.g. optometrist—not shown). The user interface 112 caninclude one or more user input devices such as but not limited to aQWERTY keyboard, a keypad, a stylus, a mouse, a microphone and the useroutput device such as an LCD screen display and/or a speaker. If thescreen is touch sensitive, then the display can also be used as the userinput device as controlled by the device infrastructure 116. Operationof the computer device 100 is facilitated by the device infrastructure116. The device infrastructure 116 includes one or more computerprocessors 108 and can include an associated memory (e.g. a randomaccess memory 114). The computer processor 108 facilitates performanceof the computer device 100 configured for the intended task (e.g. of therespective module(s) of the design tool 102) through operation of thenetwork interface 118, the user interface 112 and other applicationprograms/hardware of the computer device 100 by executing task relatedinstructions associated with lens 32 design. These task relatedinstructions can be provided by an operating system, and/or softwareapplications located in the memory, and/or by operability that isconfigured into the electronic/digital circuitry of the processor(s) 108designed to perform the specific task(s). Further, it is recognized thatthe device infrastructure 116 can include a computer readable storagemedium 114 coupled to the processor 108 for providing instructions tothe processor 108 and/or to load/update the instructions. The computerreadable medium 114 can include hardware and/or software such as, by wayof example only, magnetic disks, magnetic tape, optically readablemedium such as CD/DVD ROMS, and memory cards. In each case, the computerreadable medium 114 may take the form of a small disk, floppy diskette,cassette, hard disk drive, solid-state memory card, or RAM provided inthe memory module 114. It should be noted that the above listed examplecomputer readable mediums 114 can be used either alone or incombination.

Further, it is recognized that the computer device 100 can includeexecutable applications (such as the design tool 102) comprising code ormachine readable instructions for implementing predeterminedfunctions/operations including those of an operating system and lensdesign modules, for example. The processor 108 as used herein is aconfigured device and/or set of machine-readable instructions forperforming operations as described by example above. As used herein, theprocessor 108 can comprise any one or combination of, hardware,firmware, and/or software. The processor 108 acts upon information bymanipulating, analyzing, modifying, converting or transmittinginformation for use by an executable procedure or an information device,and/or by routing the information with respect to an output device. Theprocessor 108 may use or comprise the capabilities of a controller ormicroprocessor, for example. Accordingly, any of the functionality ofthe design tool 102 can be implemented in hardware, software or acombination of both. Accordingly, the use of a processor 108 as a deviceand/or as a set of machine-readable instructions is hereafter referredto generically as a processor/module for sake of simplicity. Further, itis recognised that the design tool 102 can include one or more of thecomputer devices 100 (comprising hardware and/or software) forimplementing the lens design method, as desired.

In view of the above descriptions of storage, the storage 114 can beconfigured as keeping the stored data (e.g. predefined curve shapeprofiles, predefined tear layer thicknesses for each of the zones 50 asselectable by the user) in order and the principal (or only) operationson the stored data are the addition of and removal of the stored datafrom the storage (e.g. FIFO, FIAO, etc.). For example, the storage canbe a linear data structure for containing and subsequent accessing ofthe stored data and/or can be a non-linear data structure for containingand subsequent accessing of the stored data. Further, the storagereceives various entities such as data that are stored and held to beprocessed later. In these contexts, the storage can perform the functionof a buffer, which is a region of memory used to temporarily hold datawhile it is being moved from one place to another. Typically, the datais stored in the memory when moving the data between processeswithin/between one or more computers. It is recognised that the storagecan be implemented in hardware, software, or a combination thereof. Thestorage is used in the design system 10 when there is a differencebetween the rate/time at which data is received and the rate/time atwhich the data can be processed.

Further, it will be understood by a person skilled in the art that thememory/storage described herein is the place where data can be held inan electromagnetic or optical form for access by the computerprocessors/modules. There can be two general usages: first, memory isfrequently used to mean the devices and data connected to the computerthrough input/output operations such as hard disk and tape systems andother forms of storage not including computer memory and otherin-computer storage. Second, in a more formal usage, memory/storage hasbeen divided into: (1) primary storage, which holds data in memory(sometimes called random access memory or RAM) and other “built-in”devices such as the processor's L1 cache, and (2) secondary storage,which holds data on hard disks, tapes, and other devices requiringinput/output operations. Primary storage can be faster to access thansecondary storage because of the proximity of the storage to theprocessor or because of the nature of the storage devices. On the otherhand, secondary storage can hold much more data than primary storage. Inaddition to RAM, primary storage includes read-only memory (ROM) and L1and L2 cache memory. In addition to hard disks, secondary storageincludes a range of device types and technologies, including diskettes,Zip drives, redundant array of independent disks (RAID) systems, andholographic storage. Devices that hold storage are collectively known asstorage media.

1. A method for generating an aspheric contact lens design forfacilitating myopia control of a cornea of a patient, the method storedas a set of instructions in memory for execution by a computer processorto: obtain measurement for degree refractive error of the eye indiopters; obtain measurement of one or more biomechanical properties ofthe cornea; define a diameter of a central zone of the contact lensbased on pupil size, the diameter being equal to or less than a selecteddimension; select a base curve profile and width for the central zonebased on the refractive error and the one or more biomechanicalproperties, the base curve profile defining a compression force strengthon the cornea when the contact lens is positioned on the eye, the basecurve profile including a central zone tear layer thickness and acentral zone radius of curvature; define a width of a reverse zoneadjacent to and encircling the central zone, the width being greaterthan 0.5 mm; select a reverse curve profile for the reverse zonecompatible with the base curve profile, the reverse curve profiledefining a tension force strength on the cornea when the contact lens ispositioned on the eye, the reverse curve profile including a reversezone tear layer thickness and a reverse zone radius of curvature; modifythe base curve profile adjacent to the reverse zone by applying aselected base eccentricity curve profile for enhancing the tension forcestrength of the reverse zone, said applying contributing to the asphericnature of the contact lens, the base eccentricity curve profileincluding an aspheric zone tear layer thickness and an aspheric zonebase eccentricity; define a width of a relief zone of the contact lensadjacent to and encircling the reverse zone; select a relief curveprofile for the relief zone, the relief curve profile moderating thetension force strength adjacent to the relief zone, the relief curveprofile including a relief zone tear layer thickness and a relief zoneradius of curvature; define a width of an alignment zone of the contactlens adjacent to and encircling the relief zone; select an alignmentcurve profile for the alignment zone, the alignment curve profileincluding an alignment zone tear layer thickness and an alignment zoneradius of curvature; and define a width of a peripheral zone of thecontact lens adjacent to and encircling the alignment zone; select aperipheral curve profile for the peripheral zone, the peripheral curveprofile including a peripheral zone tear layer thickness and aperipheral zone radius of curvature; wherein the compression forcestrength and the tension force strength of the contact lens cooperate toreshape corneal curvature in a mid-peripheral region to address themyopia control when the contact lens is applied to the eye.